Treatment of cellulosic material prior to esterification



Patented May 7, 1935 'r UNITED' STATES PATENT;OFFICE 2,000,665 i t TREATMENT oF" oELLULosIo MATERIAL PRIOR ESTERIEICATIQN j Carl J. Malm and Charles it. Fordyce; Rochester, N. Y., assignors to Eastman Kodak company, Rochester, N. L, acorporation' of New York.

1 J No Drawing. '-ApplicationFebruarylS, 1932,

Serial No. 593,870 1 12v Claims. (cllect ioi) The present invention relates to the preparation of cellulosic material for esterification'by treating it with liquid sulfur dioxide with or without a catalyst such as sulfuric acid.

The usual processes of es'terifying cellulosic material may be divided" into the two classes of the dope-forming andth'e non-dope-forming or fibrous processes. In the fibrous processes when carried out in a liquid bath it is essential'that a sufiloient amount of a non-solvent be added to render the bath non-solvent of the cellulose ester which is to be prepared. Heretofor'e the cellulosic' material employed as V the starting material for esterification has been as a"' ru1e pretreated with a -bath comprising substantially glacial acetic acid. Glacial acetic acid is a solvent .for, practically all of the organic esters of cellulose so that in the case offibrous esterification processes sufiicient non-solvent is necessary to overcome the solvent efi'ects of the acetic acid. The removaloi acetic acid, more than that which can be pressed ofi rrom thecellulose', is commercially impractical as is well known to those skilled in the art. v I t It has been previously known to pretreat cellulose with S02 in a bath substantially comprising glacial acetic acidand containing only a small amount of S02 gasdissolved therein, with or without a catalyst. However that process has the same disadvantages as far as the fibrous esterification of cellulose is concerned as the pretreatment processes of the prior art in which no S02 is employed. In addition the S02 in that process is present as an impurity in theacetic acid necessitating its removal in the reclamation of the acetic acid employed.

One subject of our invention is to reduce the manufacturing costs of cellulose acetatewhen prepared by fibrous esterification "processes. Another object of our invention is'to provide a process in which the esterification of the cellulose is accomplished within a moderate space of time and which resultsin a uniformly excellent product. Another object of our invention is to provide a process. for the pretieatment' of cellulose prior to its esterific'ation which need not contribute any re-agents to. the esterificationbath proper thus making possibletthe. em- .ployment of the particular esterification desired, whether by vapor or liquid bath, fibrous or dopefforming and in which the solvents, anhydrides diluents, catalysts etc'ldesired may be employed depending merely on the judgment and skill of the individual operator. Various otherobjects will appear'here'inafter. 1 iv w a We -have found: that cellulose can be made more readily reactive'by treating it with abath substantially comprisingliquid S02 with or 5 without a catalyst. We have found that cellulose may beprepared for esterification i without the use of glacial acetic acid in the pretreatment bath We have-found that by our invention all or substantially all of thepretreating liquid may be removed from the cellulose prior toits esterification so that the character of the esterifi'cationbath is affected little if at all cy the liquid bath employed for-the pretreatment. 'We have-found thatfby our invention the same pretreating liquid-may be easily recovered and employed for treating each suc- "cessive' batch of cellulose'which it is desired to esterify;

We have found that our pretreatment process 20 isiespecially valuable where a fibrous esterification is contemplated in which as'little nonsolvent as possible is desired. S02 is a gas at ordinary temperature' it may be substantially all removed fromthe cellulose which has been pretreated before the addition of the esterifying bath comprising the non-solvent and the 'anhydride so that the '1 amount of nonsolvent necessary is considerably" less than is the case of the fibrous est'erification of a cellulose which has been pretreated intheusual manner.

'The' "pretreatment of cellulo'selaccording to our invention is carried out preferably in a closed vessel and when temperatures above.the boiling point of the S02 are used, in a pressure vessel, If ,a catalyst; such assulfuric acid, is .presentfin the bath the cellulose may be treated at a temperature below the boiling point of the S02 at atmospheric pressure. However when the pretreatment is carried out without the catalyst it is preferred .that a higher 'tem perature be employed in order to shorten the time of treatment. In such case it would be desirable to carry out the pretreatment in an en- 415 closed pressure vessel to avoid breakage or the loss of S02. Obviously the pressure would then be aboveatmospheric. If desired the pretreatment could :however be carried outv in a refluxing ,ap-. para-tus in'which case the condensing portion must necessarily be at a ratherlow temperature such as may be obtained by the circulation of a brine having a temperature "of 0 F. H At' the end of the pretreatment the S02 may be removed from the cellulose 'b'y' distillation which due to the low boiling point of the S02 is a relatively simple matter.

It is not known whether sulfur dioxide has the same effect on cellulose in the pretreatment as does acetic acid or not but the pretreated cellulose is readily esterified and gives cellulose esters of extraordinary whiteness. The fact that liquid S02 may'be employed in the pretreatment of cellulose is remarkable when it is considered that sulfur dioxide bears no relation chemically to glacial acetic acid. which has been usually employed heretofore. v I

One feature of our invention which is of v importance from the economic standpoint isthat' the S02 which is employed in the pretreatment of cellulose may be recovered in a pure form in practically its entirety, from theme treated cellulose and thus the same S02 maybe As. has been pointed. out above, our pretreat- I ment may be employed to prepare cellulose for either dope-forming or. fibrous esteriflcation processes, and the esterification bath, may be of any composition closed in the prior art. For example our pretreated cellulose may be employed for either the preparation of. cellulose acetate by the use of acetic anhydrid, or acetyl chlorid or it may be.- employed as the starting material for the preparation of higher esters (either simple or mixed) for instance according to one of the processes disclosed in U. 3. Patents Nos. 1,800,860 and 1,880,808 of Clarke &

Malm. I v

The following example illustrates the application of our pretreatment to a. process for the fibrous esterification of cellulose:

50 lbs. of cotton linters was mixed with. 290. lbs. of liquid S02 containing 2 lbs. of sulfuric acid and the whole was. maintained at a temperature of 10 F. for 10 hours. The excess S0: was drained oifand the temperature was. then allowed to rise until the. S01 remaining was distilled off. This. S02 was, condensed and em} ployed in a subsequent pretreatment.

The pretreated. cellulose was. .then addedto a mixture of 150. lbs. of. acetic anhydrid and 630 lbs. of carbon. tetrachloride and the mass was maintained at a maximum temperature of 40 C. until a sample showed that, the ester formed was soluble in a mixture consisting of chloroform-ethyl alcohol containing 15% of the latter.

The use oi." carbon tetrachlorid as the nonsolvent in the example is merely illustrative as any of the known non-solvents such as benzene or a higher ether as disclosed "in Malm and Fletcher application Serial No. 590,508, filed February 2; 193-2 may be employed.

The cellulose which is employed as the startingmaterial may beany of the usual types disclosed in theprior art such as pulp, linters or other forms. This starting cellulose. is preferably one which has been bleached. and. ovendried and which contains not more than about 1%. of moisture.

Various other modifications. of our invention which are: apparent to those shined: in the. art such as. the use of. dilrerent catalysts, variations in proportions, time of treatment, etc. are within the scope of the present invention. For example the liquid S02 might be mixed with nonsolvent such as carbon tetrachlorid, a higher ether or the like and the pretreatment of the cellulose would take place in that bath with or without a. catalyst. After the pretreatment the S02 may be easily removed from the carbon tetrachloride by allowing the mixture to come to room temperature. The S02 distills off and can be. collected for reuse. The cellulose remaining isv wet with carbon tetrachlorid (or the other non-solvent employed) and is eminently fitted for use as the starting material in a fibrous esteriiication bath.

If desired the carbon tetrachlorid could also be, removed from. the cellulose after this type of pretreatment by mild heating at a temperature above. the boiling point of the tetrachlorid and below that point at which the cellulose is scorched or affected detrimentally. This cellulosefrom which the pretreating liquid is removed may then be employed inv dope esterification processes.

Obviously if desired a. small amount of glacial acetic acid might also be dissolved in the liquid S01:v to. form a pretreatment bath, from which at the. end of the pretreatment the S02 could be all removed. This type of pretreatment bath is adapted for the preliminary treatment of cellulose for dope esterification processes asthe protreated cellulose in this case has a certain content of glacial acetic. acid homogeneously distributed therethru.

We'claim' as our invention:

1. The preparation of cellulose for e'sterification'whichcomprises pretreating it with a bath containing liquid sulfur dioxide as the principal active 'pretreating agent preliminary to the application of esterifying reagents thereto.

2. The preparation of cellulose for esterification which comprises pretreating it with a bath containing a predominating proportion of liquid sulfur dioxide preliminary to the application of esterifying reagents thereto.

3'. The preparation of cellulose for esteriilcation which comprises pretreating it with a bath containing a predominating proportion of liquid sulfur dioxide and a small amount of catalyst to. the application of esterifying reagents thereto.

4. Thepreparation of cellulose. for esterification which comprises pro-treating, it with a bath containing a. predominating proportion of liquid sulfur dioxideand a small amount of sulfuric acid preliminary to the application of esterifying reagents thereto.

5. Thepreparation of cellulose for ester'ification which comprises pretreating it with a bath containing a predominating proportion of liquid sulfur dioxide and a small amount of sulfuric acid ata temperature below the boiling point of the sulfur dioxide preliminary to the application of esterifying" reagents thereto.

6. In'the esterification of cellulose the steps which comprises pretreating the. cellulose with a bath containing a predominating proportion of liquid sulfur dioxide under conditions whereby the sulfur dioxide retains its liquid state and then restoring normal conditions. so that the S02 may evaporate off from the cellulose.

71.. A. process for the fibrous esterification of cellulose. which comprisesv treating the cellulose with a bath comprising mainly liquid sulfur dioxide, removing the sulfur dioxid' and then esterifying the cellulose in a bath substantially comprising a fatty acid anhydrid, a non-solvent and a catalyst. I

8. A process for the fibrous acetylation of eellulose which comprises treating the cellulose with a liquid sulfur dioxide bath, removing the sulfur dioxide and then esterifying the cellulose in a bath substantially comprising acetic anhydrid, a non-solvent and a catalyst. V

9. In the preparation of cellulosic materials for esterification the'cyclic process of treating the cellulosic material with liquid sulfur dioxide, then draining off some or the liquid sulfur dioxide from the cellulose and distilling oil the remainder, and treating a second batch of cellulosic material with a bath substantially comprising the recovered sulfur dioxide in liquid form.

10. The preparation of cellulose for esterification which comprises pretreating it with a bath containing a predominating proportion oi! liquid sulfur dioxide at a pressure above atmospheric.

11. In the process of making cellulose acetate, the step which comprises pretreating the cellulose to be acetylated with a preliminary bath containing a predominating proportion of liquid sulfur dioxide. 5}

12. A process for the fibrous esterification of cellulose which comprises treating the cellulose with a bath comprising mainly liquid sulfur dioxide, removing the sulfur dioxide and then esterifying the cellulose.

CARL J. MALM. 4 CHARLES R. FORDYCE. 

